This invention relates, in general, to diesel engines and, more particularly, to an insert for a combustion chamber of diesel engines. The insert to be received within the cylinder head within the combustion chamber of a diesel engine must have high refractory properties due to the exposure to hot combustion gases and because of the required sizing precision. Heretofore, such inserts have been produced either by the investment casting process or by the cutting of round bar stock. Although the investment casting process has recently been developed to such an extent that complex and close controls of high sizing accuracy and crystalline granularity can be accomplished in producing refractory castings such as the gas turbine parts of a jet engine or the like, such process is not suitable for the production of inserts for the combustion chambers of diesel engines because of the numerous complex steps which would extend the casting period with attendant high production cost. Such inserts requiring high refractory properties must, necessarily, be fabricated of refractory steel, and such is, in general, relatively amenable to the cutting process. Moreover, the cutting process of the round bar has such a remarkably low yield as to make the costs for the material and for effecting the working procedures uneconomical. These drawbacks are especially involved wherein the inserts are provided with an injection port of oblique character, which ought to be produced by the cutting process as it is quite difficult to form such port. More specifically, this difficulty is most apparent in the machining process since the drill must usually be turned in such a manner so that it is difficult to form a hole having a shape other than round. Accordingly, the machining process is not suitable for forming a hole having other than a round shape, such as, for instance, square, rectangular, oval, or semi-circular; and this is particularly true for forming an oblique opening, that is, one whose major axes is inclined with respect to the work surface. Such oblique opening could be worked by the three-dimensional feeds of the table of a milling machine. If the material to be cut is made of refractory or extremely hard material, the life of the cutting tool is invariably short and the cutting operation requires a lengthy period whereby production costs are materially increased. Therefore, it has been found that the machining process is not suitable for mass-produced products such as the aforesaid inserts. The cutting tools are considerably worn during the process of cutting hard or highly refractory materials so that the maintenance of such tools, as well as the need for constant replacement, adds further to the production cost. Also, from the standpoint of sizing accuracy, since the diameter of the cutting tool is gradually decreased through use, the spindle position must be accordingly continually adjusted. Although the incorporation of an appropriate correcting device is not impossible, the cost and price of the milling machine as a whole becomes so high as to make the machining process prohibitive.
A prior art effort for producing an insert having an oblique injection port has been attempted by causing the insert material to be of multi-part character and then assembling the discrete parts into a whole after the injection port having the inclined hole has been cut. However, this method is inadequate since the component, individual parts each require cutting and working, and then welding and finishing steps. Manifestly, with such discrete elements, the method steps are multiplied and thus cause problems in material yield and in production cost.
In another effort to produce an insert of the character stated, there has been proposed the process of inserting into a die a disc-shaped or cylindrical refractory steel blank containing less than 0.06% of carbon, by cold- or hot-compressing the steel blank between a punch and a counter-punch to thereby compress the blank into a generally center-recessed shape and with the formation of a hole in the bottom. Since the refractory steel is cold- or hot-forged, the method thus disclosed is adequate in sizing accuracy, productive, and reliable as an intermediate product is formed before the injection port has been developed. However, this method requires considerable time and costly labor in the hole-forming process because the conventional method is adopted to form the hole in such intermediate product.
With a view to overcoming the problems stated, the present invention has been conceived and developed to produce an insert at low cost by reducing the portion to be formed with a hole, while facilitating the hole-forming step by developing a unique recess having a similar shape as the injection port either in the outer side or in the outer and inner sides or such reduced portion simultaneously with the forming of the insert work material.
More specifically, the present invention contemplates the provision of a method for producing an insert for diesel engine combustion chambers which essentially comprises the steps of inserting a cylindrical work blank into a die; cold- or hot-compressing said work blank between a punch and counter-punch to develop a center-recessed shape; forming an oblique recess, that is, one axially inclined to the longitudinal axis of the workpiece in the outer side of the base of such shape at such a position as to correspond to the injection port of the insert to be formed simultaneously with or after the compressing step; and forming a corresponding oblique opening in said oblique recess.